1. Field of the invention
This invention relates to a process for isomerizing saturated hydrocarbons. More particularly, it relates to a process for isomerizing a saturated hydrocarbon or a saturated hydrocarbon mixture to convert the same to a more highly branched saturated hydrocarbon or hydrocarbon mixture.
The present invention is also concerned with isomerizing alicylic hydrocarbons contained in petroleum hydrocarbons to convert the same to other isomers.
Furthermore, it is also concerned with ring-opening alicyclic hydrocarbons contained in petroleum hydrocarbons to convert the same to aliphatic hydrocarbons. As a manner in which the invention is utilized it is also concerned with conversion of aromatic hydrocarbons contained in petroleum hydrocarbons by saturation of the aromatic rings with hydrogen to alicyclic hydrocarbons as well as to isomerization or ring-opening to aliphatic saturated compounds of the resulting alicyclic compounds.
2. Description of the prior art
Various properties are required for gasoline fuel, including distillation characteristics, being free from corrosiveness, and appropriate volatility. Among them, high octane value is regarded to be critical.
Aromatic hydrocarbons, olefin hydrocarbons and highly branched saturated hydrocarbons are known to posses high octane values. The highly branched hydrocarbons are superior to the other hydrocarbons in that there is with the former less difference between the octane value according to the research method and that according to the motor method, that is, due to the lower sensitivity of the hydrocarbons.
The gasoline is a mixture of a variety of hydrocarbon compounds. The highly volatile of these, with boiling points below 85.degree.C., are ordinarily olefin and saturated hydrocarbons having low molecular weights for the most part but most are saturated hydrocarbons.
For use in the highly developed gasoline engine is needed a gasoline containing in the low-boiling component low molecular weight saturated hydrocarbons possessing high octane values such as, for example, isopentanes and isohexanes, because gasoline is required to have high octane values throughout all the distillates.
In petroleum refining industry there have been divised and put into practical use various processes for isomerizing saturated hydrocarbon compounds to produce highly branched hydrocarbon compounds.
All of these isomerization processes are catalytic isomerization processes effected by the use of a catalyst. The catalysts used in these processes may be broadly classified into three classes: Metal halide catalysts of Friedel-Crafts type such as aluminium chloride or bromide used in combination with anhydrous hydrogen chloride or bromide; so-called dual functional catalysts comprising a metal component of hydrogenating function such as nickel, platinum or palladium carried on a refractory oxide such as alumina or silica-alumina; and platinum-alumina-halogenide composite catalysts.
Using a catalyst mainly composed of a metal halide such as aluminium chloride in the isomerization reaction of hydrocarbons containing more carbon atoms than pentane side reactions occur such as polymerization, condensation, disproportionation and cyclization with rapid deterioration of the catalyst. Moreover, the catalyst, which is highly corrosive, requires the use of a corrosion-resistant alloy for the main parts of the equipment. In addition, it is disadvantageous that the aluminium chloride sludge withdrawn from the equipment should be made harmless by means of, for example, neutralization or combustion.
On the other hand, so-called dual functional catalysts such as platinum-alumina, which are free from the afore mentioned disadvantages of aluminium-chloride catalyst, require use of a relatively high temperature in carrying out the reaction in order to attain a practically high reaction rate.
As well known, the lower the temperature the more favorable is the composition of paraffin hydrocarbon isomers at thermodynamic equilibrium to the highly branched isomer. Consequently, octane value of the product in the process using a dual functional catalyst, which requires a high reaction temperature, is controlled by the thermodynamic equilibrium in the same way as is the composition of isomers in the product.
Although composite catalysts of platinum-alumina with impregnated aliminium chloride thereupon by such a means as sublimation or impregnation, which are considered to be catalysts with combined merits of aluminium-chloride catalyst being active at low temperatures and of binarily functional catalyst being free from corrosiveness, requiring no activator such as hydrogen chloride and generating no harmful sludge, have been found to be effective at relatively low temperatures with little side reactions and are superior to the former two, they are disadvantageous in that the catalyst will be poisoned unless water content of the starting hydrocarbon is maintained below a few p.p.m. as well as regeneration of the deteriorated catalyst cannot be easily made.
Recently, crystalline aluminosilicate of zeolite type have drawn attention as a carrier being superior to alumina or silica-alumina. Catalysts composed of combination of platinum and crystalline aluminosilicate of zeolite type have been found to exert high catalytic activities. According to the descriptions by J. A. Labo, P. E. Pickart and R. L. Maize, catalyst MB 5390 manufactured by Department of Molecular Sieve Products of Linde Corporation, Tonawanda, N.Y., U.S.A., a division of Union Carbide Corporation, is water-proof and effectively used in the isomerization reaction of n-pentane and n-hexane at a reaction temperature from 335.degree. to 340.degree.C. [Industrial and Engineering Chemistry Vol. 53, No. 9, P. 735 (1961)]. The catalyst has been demonstrated on the basis of X-ray diffraction pattern and chemical analysis to be Molecular Sieve Y decationized and carrying a small amount of palladium [Noboru Yamamoto, Kataundo Fujii and Yoshitaka Damaru, Journal of Petroleum Society of Japan, vol. 9, No. 7, p. 531 (1966)].
In order to obtain hydrocarbons of high octane values, however, catalysts that are effective at lower temperatures are naturally desired.
Another crystalline aluminosilicate of zeolite type which may be used as a catalyst is mordenite. Mordenite catalysts including metallic hydrogenation component such as platinum or palladium, are effective at somewhat lower temperatures (of. the comparative examples below) but, with respect to improvement in octane value, there is a need for catalysts that are effective at even lower temperatures.
In order to enhance activities of platinum-alimina, palladium-alumina and other dual functional catalysts in the isomerization reaction, various methods are known; (1) addition of aluminum chloride by sublimation or impregnation, (2) introduction of halogens by reacting the catalyst with halogenating agents such as CCl.sub.4, S.sub.2 Cl.sub.2, SOCl.sub.2, PCOl.sub.1, or the like. An experiment has disclosed that these catalysts are effective at a lower temperature, viz., at 165.degree.C. All of these catalysts, however, are hygroscopic as highly as is aluminium chloride as mentioned earlier and, on contacting with moisture, are reduced in catalytic activity so much that recovery of the activity by conventional means such as drying and calcination will be impossible.
On the other hand, we have discovered a method of introducing onto crystalline aluminosilicate of zeolite type a halogen by the reaction with a halogenated hydrocarbon (West German Patent Publication No. 2,010,551), wherein only the application to crystalline aluminosilicate of faujasite type is disclosed but no embodiment on mordenite.
Both mordenite and faujasite are classified in mineralogy under aluminosilicate of zeolite type, but the two are different in properties such as a chemical composition, crystal structure and reactivity with halogenated hydrocarbon. In particular, mordenite containing far smaller portion of aluminium than that in faujasite is not subjected to halogenation so readily as the latter or, if halogentated, to a halogen content as high as the latter.
For example, according to an experiment on halogenation of a commercially available reforming catalyst composed of substantially 100% alumina carrying platinum with CCl.sub.4 (the third World Petroleum Congress, Amsterdam, 1964, by A. G. Goble and P. A. Laurance), there has been easily obtained a catalyst containing 13.6% chlorine. As we have previously demonstrated, treatment of zeolite of faujasite type with CCl.sub.2 F.sub.2 yields zeolite containing 0.12% fluorine and 0.16% chlorine.
As set forth above, halogenation of mordenite with very low content of aluminum as compared with zeolite of faujasite type is difficult to conduct and for the same reason the combination with a halogen in an amount sufficient to improve catalytic activity has been unexpected; molar ratio of silica to alumina (SiO.sub.2 /Al.sub.2 O.sub.3) is from 2 to 5 with the latter and above 9 with former. Such a case of halogenation has not been known at least regarding mordenite.